Phased array antennas are well known in the prior art. For phased array antennas, transmission lines in the feed networks of phased antenna arrays can be used to divide equally the power in, and to phase appropriately each of the antenna elements in the phased array.
One challenge in phased array antenna design can be to minimize the respective physical footprint occupied by the supporting RF circuits (which includes the transmissions lines). The culprit here can often be the phase delay lines. Phase delay lines, such as conventional microstrip transmission lines (TL's), must be designed to be a certain physical length in order to achieve a given desired phase shift at a given design frequency. This phase dependency on length can result in lines that must be “meandered” in order to maintain a small footprint, as in passive phased arrays. In addition, this length dependency on phase can result in increasing phase slopes, as the lines increase in physical length. This creates a variety of different problems, including an expanding physical footprint. Another problem can be a limitation in phase bandwidth that arises from TL's of different physical lengths having different phase slopes.
Another design consideration for phased array antennas is the phase slope, i.e., the change in phase over the frequency band of interest. For conventional TL's, the slope of the phase response is a function of the physical length of the transmission line. As a result, as length of the conventional TL's increase, the phase slope can also increase. When conventional TL's of different lengths exhibit this phase slope behavior, this can lead to a variety of performance issues for the antenna. More specifically, at the design frequency of the antenna, all of the TL's have the same phase while outside of the design frequency each of the TL's begin to exhibit increasingly different phase values. The increasing different phase values (due to the drift in phase slope) can result in a radiation pattern for the array that can begin to diverge and scatter as a function frequency, since each antenna element in the array no longer maintains a uniform phase difference. This phenomena is often referred to as “beam squint”. Beam squint is typically an undesirable effect for phased array antennas, and should be avoided.
To avoid beam squint, hybrid metamaterial transmission Lines (MTM-TL's) can be used. MTM TL's can combine the negative phase (or phase delay) of conventional, right-handed (RH) transmission lines, with the positive phase (phase advance) exhibited by left-handed (LH) transmission lines. MTM-TL's can be designed from combinations of right-handed TL's and Composite Right/Left Hand (CRLH) TL's. The single CRLH unit cells, in which the CRLH TL's are composed of, are of the same physical length but have different phase and phase slopes associated with each. These Composite Right/Left Hand (CRLH) transmission lines can achieve a negative phase velocity in the left-hand frequency band, and a positive phase velocity in the right-hand frequency band. Thus arbitrary phase-shifts can be achieved, zero and non-zero, both positive and negative phase across the length of the transmission line, independent of its physical length.
The prior art using conventional transmission lines and MTM TL's does not disclose constructing a family of MTM TL's that can achieve both equal phase and phase slope response. The significance of these engineered MTM-TL's is their improved performance over a wider bandwidth, and their ability to occupy smaller footprints, because they can be routed more effectively within tightly fitting phase shifting networks for use in various RF and phased array antenna applications.
In view of the above, it is an objective of the present invention to provide a plurality of MTM-TL's that minimizes beam squint for a phased array antenna. Another object of the present invention is to provide MTM-TL's for a phased array antenna that each have a substantially equal phase slope response over a broadband frequency range. Still another object of the present invention is to provide MTM-TL's for a phased array antenna that have a smaller physical footprint relative to a TL's for the phased array antenna of same electrical size. Yet another object of the present invention is to provide MTM-TL's for a phased array antenna which have greater power out when compared to conventional TL's having the same physical size. Another object of the present invention is to provide MTM-TL's for a phased array antenna that are easy to manufacture in a cost effective manner.